The Microbiome
Humans are made up of not only human cells, but trillions of bacterial cells. Bacteria often get a bad rap and are associated with dirtiness and disease. However, many bacteria are necessary for humans to thrive. The human intestinal tract contains 100 trillion bacteria (that’s 10 to 100 times more bacteria than human cells).[1] Even more impressive is the genetic information contained in these bacterial communities. The Human Genome Project has identified roughly 20,000 protein-coding genes in our DNA and 100,000 potential genes. The Human Microbiome Project, a more recent effort, has identified 8 million genes in the bacterial communities of the human gut.[2] No two microbiomes are the same. Each individual has a unique composition of bacteria, both in number of cells and diversity of bacterial species, that can affect many aspects of his or her health. Bacterial diversity varies for several reasons, but diet is a key factor in determining microbiome composition.[3] Microbiota composition is a good representation of the lifestyle and environmental history of an individual.[4] This composition is dynamic and fluid. It continues to change throughout one’s lifetime in response to antibiotics, diet, environment, and possibly dozens of other factors we have yet to discover. Probiotics are live organisms that exert a health benefit on the host by altering the gut microbiome.[5] Many new research efforts aim to gain an understanding of how probiotic implementation (and subsequent microbiome alteration) affects mental health outcomes. These probiotics that can affect the brain and thus mood are called psychobiotics.
Probiotics & Gut Biodiversity
There are a number of species that dominate the microbiome. Your unique dominant species is called your “enterotype”. Enterotypes are a relatively new concept and way of classifying people, so clinical application of these enterotypes is preliminary. The three enterotypes recognized by researchers are Type 1 (Bacteroides dominant), Type 2 (Prevotella dominant), and Type 3 (Ruminococcus dominant).[6] Interestingly, these enterotypes appear to be unaffected by age, sex, weight, and nationality.[7] Diet, immune health, and neuroendocrine health do appear to affect microbiome diversity, however. For example, people suffering from autism and autism-spectrum disorder often lack certain strains of bacteria present in healthy individuals.[8] Researchers have bred mice with no gut bacteria (termed GF or germ-free mice) to examine their health outcomes. These mice typically have an underdeveloped immune system and exaggerated nervous system responses.[9] It is hypothesized that the presence of bacteria in the gut teaches the immune system to differentiate between harmful pathogens and helpful bacteria.[10] Dysbiosis, or an imbalance in microbiota, is associated with chronic low-grade inflammation, metabolic disorders, gastrointestinal disorders, and increased pathogenesis.[11] Probiotics are commonly used to restore balance after antibiotic exposure, but more research suggests that they should be implemented as adjuvant or preventative therapy for a variety of conditions.[12] Probiotics can decrease the number of pathogens in the body[13], modulate microbiome diversity, and alter metabolic function of existing bacteria.[14]
Stress: Bad for Bacteria and Their Hosts
It is apparent that bacteria can influence the brain (and possibly vice-versa), though the exact mode of gut-brain communication via microbes is only partly known.[15] The microbiome begins to colonize immediately after birth and is typically completely established within a year.[16] It appears that neonatal stress can alter the microbiome indefinitely.[17] Maternal separation (a major stressor for infants) has been shown to change and decrease gut microbiome diversity.[18] Stress also increases intestinal permeability, which allows bacteria to cross from the gut into the bloodstream and cause an immune response.[19] Not only does stress alter microbiome diversity—bacterial composition can change physiological stress responses in the body. GF mice have an exaggerated stress response[20], which can cause a cascade of other physiological problems. Probiotic treatment has been shown to reduce or normalize cortisol levels.[21] The HPA-T axis, which controls the body’s stress response, can be downregulated in the presence of probiotics.[22] Stress on the HPA-T axis can cause a variety of mental and physical health problems, so this downregulation by probiotic supplementation is very promising as an adjunctive treatment option for a variety of stress-related conditions.
Psychobiotics
Psychobiotics are probiotics with mental health benefits. It is apparent that gut bacteria influence the body in many ways, but the newest and perhaps most exciting application of microbiome manipulation is supplementation with psychobiotics. Studies have shown that probiotic treatment improves anxiety and depression.[23] Gut bacteria produce neuroactive substances and their precursors as byproducts, which in turn can influence mood and cognition in the host.[24] Some of the major neurotransmitters affecting mood and mental health are GABA, serotonin, dopamine, and norepinephrine. The table below contains some common types of bacteria in probiotic supplements and the neurotransmitter(s) they modulate.[25]
| Bacillus | Dopamine
Norepinephrine |
| Bifidobacteria | GABA |
| Enterococcus | Serotonin |
| Streptococcus | Serotonin |
| Escherichia | Serotonin
Norepinephrine |
| Lactobacilli | GABA
Acetylcholine |
Probiotics also alter neuron excitability and health. Mice with normal gut bacteria have almost three times as much serotonin as GF mice.[26] Probiotics have been shown to alter GABAA receptors, the same receptors that drugs such as Xanax and alcohol affect.[27] One study found probiotic supplementation to be as effective as citalopram (a common antidepressant) at treating depression.[28] It is estimated that by 2030, depression may be the leading cause of disability in the United States.[29] Finding new and effective treatments for mental health problems is a huge area of interest for researchers right now. Current studies show promising results for probiotic implementation in alleviating symptoms of anxiety and depression. Maintaining a healthy microbiome is pivotal in mental and physical health. See the links below to find out how you can keep your gut healthy and your mind happy!
To learn more about Sanesco’s testing for neurotransmitter and hormone imbalances, please contact us.
Resources
[1] Foster, J. A., & Neufeld, K. M. (2013). Gut–brain axis: how the microbiome influences anxiety and depression. Trends in Neurosciences, 36(5), 305-312. doi:10.1016/j.tins.2013.01.005
[2] Hemarajata, P., & Versalovic, J. (2013). Effects of probiotics on gut microbiota: mechanisms of intestinal immunomodulation and neuromodulation. Therapeutic Advances in Gastroenterology, 6(1), 39–51. http://doi.org/10.1177/1756283X12459294
[3] Cryan, J. F., & Dinan, T. G. (2012). Mind-altering microorganisms: the impact of the gut microbiota on brain and behaviour. Nature Reviews Neuroscience, 13(10), 701-712. doi:10.1038/nrn3346
[4] Foster, op. cit.
[5] Cryan, op. cit.
[6] Hemarajata, op. cit.
[7] Hemarajata, Ibid.
[8] Hsiao, E. Y., McBride, S. W., Hsien, S., Sharon, G., Hyde, E. R., McCue, T., … Mazmanian, S. K. (2013). The microbiota modulates gut physiology and behavioral abnormalities associated with autism. Cell, 155(7), 1451–1463. http://doi.org/10.1016/j.cell.2013.11.024
[9] Foster, op. cit.
[10] Sarkar, A., Lehto, S. M., Harty, S., Dinan, T. G., Cryan, J. F., & Burnet, P. W. (2016). Psychobiotics and the Manipulation of Bacteria–Gut–Brain Signals. Trends in Neurosciences, 39(11), 763-781. doi:10.1016/j.tins.2016.09.002
[11] Hemarajata, op. cit.
[12] Steenbergen, L., Sellaro, R., Hemert, S. V., Bosch, J. A., & Colzato, L. S. (2015). A randomized controlled trial to test the effect of multispecies probiotics on cognitive reactivity to sad mood. Brain, Behavior, and Immunity, 48, 258-264. doi:10.1016/j.bbi.2015.04.003
[13] Huang, R., Wang, K., & Hu, J. (2016). Effect of Probiotics on Depression: A Systematic Review and Meta-Analysis of Randomized Controlled Trials. Nutrients, 8(8), 483. http://doi.org/10.3390/nu8080483
[14] Hemarajata, op. cit.
[15] Hsiao, op. cit.
[16] Cryan, op. cit.
[17] Foster, op. cit.
[18] Cryan, op. cit.
[19] Foster, op. cit.
[20] Sarkar, op. cit.
[21] Foster, op. cit.
[22] Sarkar, op. cit.
[23] Hsiao, op. cit.
[24] Steenbergen, op cit.
[25] Sarkar, op. cit.
[26] Hemarajata, op. cit.
[27] Cryan, op. cit.
[28] Sarkar, op. cit.
[29] Huang, op cit.
Clinical Contributor
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Disclaimer: The information provided is only intended to be general educational information to the public. It does not constitute medical advice. If you have specific questions about any medical matter or if you are suffering from any medical condition, you should consult your doctor or other professional healthcare provider.
